This invention relates to a method and system of producing phase front distortion of electromagnetic waves.
One of the prior art methods and systems of producing phase front distortion included two repeaters, each with two antenna "horns". One repeater (the inner one) receives with the right horn, amplifies the signal and transmits from the left horn. The other repeater receives with the left horn, amplifies, phase shifts 180.degree. and transmits from the right horn. To perform properly (relatively frequency independent) the path lengths of the two repeaters from the center of the source, through the repeater and back to the source must be identical except for the desired phase difference, in this case 180.degree., but several problems occur with this method and system: unwanted repeater antenna coupling, phase (path length) instability in the amplifiers, and phase instability in the path lengths between the amplifiers and the antennas.
Also in the prior art a two-horn system was designed to solve the antenna isolation problem and perhaps the phase instability problem in the paths to the antennas. In the two-horn method the two repeaters share antennas with a circulator used to isolate the signal received by one repeater from the signal transmitted by the other repeater. However, the two-horn method also has problems: circulators are not available with adequate isolation and the phase instability problem of the amplifiers remains.
It is to be noted that the aforementioned four-horn, and two-horn configuration may be also referred to as cross-eye configurations. A study of these two configurations were conducted and a brief summary of the results is presented.
The four-horn configuration operates as follows: the victim radar's transmitted signal is received in receiving antenna one. It is then amplified and repeated back through transmitting signal antenna one. Simultaneously, the victim radar's transmitting signal is also received in receiving antenna two. It is amplified, phase shifted 180.degree., and repeated back through transmitting antenna two. This setup allows the relative path lengths of the repeated signals to remain unchanged even if the geometry changes. The two-horn configuration uses circulators to eliminate two of the horns from the four-horn configuration. Sufficient circulator isolation is the primary requirement for the success of this configuration's operation. Preference was given to the two-horn version of cross-eye rather than the four-horn setup, because of the less severe phase-match problems associated with it (i.e., matched antenna-phase patterns, transmission-line characteristics, etc.). Although the two-horn implementation appeared more promising from the phase-matching standpoint, the circulator isolation requirement is difficult to achieve.
The present invention provides a method and system which eliminates some of the serious problems. Matching phase and gain in a pair of TWT (travelling wave tube) amplifier chains are a serious problem in both the four- and two-horn systems and meeting the antenna-isolation and circulator-isolations requirements of these respective systems are also a serious problem. The system described hereafter, multiplex "cross-eye", eliminates all the aforementioned problems.